Brake Caliper Question

[sshukes]

I've removed the rear brakes from my 76 fiat and was wondering how freely the piston in the caliper should be able to move? Right now it goes in some distace but then I have to force it in further. Also, if it's too tight any ideas on how to loosen it? I've seen some people try to sand it down but was wondering what anyone else has done. Thanks

[azruss]

the rear piston is retracted by turning it CCW. use the slot like a screwdriver slot. A flat file makes a good screwdriver here. It does not turn in easy as it will require a crescent wrench with the file. The piston should retract about a 1/16" short of being flush with the casting.

[DieselSpider]

It screws on to the auto adjuster for the parking brake via the slot on the face of the piston. As mentioned a flat file and adjustable wrench work well to turn them. Remeber to leave the slots turned so you can slide the pin in the brake pads through them.

[sshukes]

Thanks for the feedback. So I understand this more, if I have the caliper completely out, and taken apart, the piston should not be able to move freely through the bore . Right?

[onetofour]

With most calipers the bore should have a rubber seal ring inside that will seal the piston to the bore making it hard to push the piston in which is normal. Without the seal the piston will just slide in freely although the tolerance is very tight and precise.

If it was me I wouldn't sand down the pistons but instead buy new stainless pistons (if available).

---

oops - just read that you're talking about the rear brakes. Should still apply....

[azruss]

If you are just looking to clean of the pistons, rather than sand i recommend polishing with a cotton wheel and stick compound.

[DieselSpider]

Thanks for the feedback. So I understand this more, if I have the caliper completely out, and taken apart, the piston should not be able to move freely through the bore . Right?

The rears do not move freely, they are mounted on a threaded stud attached to the parking brake lever. The are either spun in or out using the slot in the piston face. There is a spring clutch inside the piston to allow some level of self adjustment as the pads wear and free play so the brakes can engage so you will be able to move them a little however you have to spin the entire piston to collapse it into the caliper when replacing the pads or to remove the piston to install a rebuild kit.

Unless the brakes have not been flushed for a very long time so that the pistons have rusted and pitted you should only need to wipe them down with a coarse rag soaked in brake cleaner. If pitted on the sides the pistons will need to be replaced however I have not found a source of replacement pistons possibly others have.

Pay attention to the moving parts inside the piston as those can become rusted and may need to be disassembled in order to clean them up. Watch out as there is a bearing cage with lose ball bearings inside the piston that are easily lost once you remove the clip and pull the adjuster out.